The present invention relates to a method for making polyetherimides by effecting reaction between aromatic bis(ether anhydride) and an organic diamine under solution polymerization conditions. More particularly, the present invention relates to the use of certain quaternary salts of Group Va elements as polymerization catalysts for making aromatic polyetherimides.
Prior to the present invention, certain catalysts, such as sodium chloride and ferric sulfate, as shown by Williams et al, U.S. Pat. No. 3,998,840, assigned to the same assignee as the present invention, were used to enhance the rate of formation of polyetherimide under melt polymerization conditions. Although valuable results were achieved by such procedures, it was found that the aforementioned catalysts were either less effective or not effective when utilized for making polyetherimides from aromatic bis(ether anhydride) and organic diamine under solution polymerization conditions. In addition, the presence of chloride ion may interfere with the use of such polyetherimide in electrical applications. Various metal compounds were also used to catalyze polyetherimide formation by imideamine exchange reactions, as shown by U.S. Pat. No. 3,847,870, Takekoshi and U.S. Pat. No. 3,850,885, Takekoshi et al, assigned to the same assignee as the present invention. However, the nature of the polymerization is quite different from polyetherimide formation by the melt polymerization of aromatic bis(ether anhydride) and organic diamine, which is amine-anhydride interaction rather than imide-amine exchange.